Glutamine metabolism stimulates intestinal cell MAPKs by a cAMP-inhibitable, Raf-independent mechanism

Background & Aims: Infectious diarrhea caused by viruses plus enterotoxigen ic bacteria is often more severe than diarrhea induced by either pathogen a lone. We postulated that the increased cell adenosine 3',5'-cyclic monophos phate (cAMP) concentration observed during infection by enterotoxigenic org anisms retards the intestinal repair process by blocking activation of mito gen-activated protein kinases (MAPKs) in proliferating intestinal cells, Me thods: We evaluated the effects of glutamine on MAPK activity, thymidine in corporation, and cell number in glutamine-starved and -sufficient rat intes tinal crypt cells (IEC-6), Results: In glutamine-starved cells, 10 mmol/L g lutamine in the absence of serum stimulated [H-3]thymidine incorporation 8- fold, This effect was inhibited by 60% with 8-(4-chlorophenylthio) (8-CPT)- cAMP (100 mu mol/L) + isobutyl methylxanthine (100 mu mol/L). In cells not starved of glutamine, glutamine stimulated thymidine incorporation by 3-fol d, and 8-CPT-cAMP completely blocked the mitogenic effect, Inhibition of pr oliferation by cAMP persisted for at least 68 hours after cAMP removal, In vitro kinase assays showed that glutamine signaling requires an intact ERK (extracellular signal-related kinase) pathway in unstarved cells. In starve d cells, at least one other pathway (JNK) was activated by glutamine, and t he mitogenic inhibition by 8-CPT-cAMP was incomplete, Other intestinal fuel s (glucose and acetate) were not mitogenic, Conclusions: Increased levels o f intracellular cAMP inhibit ERKs but only partially reduce glutamine-stimu lated proliferation in enterocytes adapted to low glutamine.